This invention relates to fluid flow rate control devices, in particular valves, wherein a partial-revolution DC motor controls the rotation of a poppet-carrying rotor within the valve and means are provided for effecting axial translation of the rotor in response to its rotation. Specifically, this invention relates to magnetic biasing of the rotor to one extreme axial position thereof wherein the poppet closes the valve structure and to an arrangement of elements which provide axial translation of the rotor and poppet in response to rotation of the rotor.
Fluid flow rate control devices of the type to which this invention is related provide a modulating valve to regulate the flow of such fluids. The fluids may be corrosive and/or flammable in nature and therefore the portions and elements of the valve in contact with the fluid must be corrosion resistant and, to the extent possible, should avoid small fluid passages and relative movement between closely toleranced elements whereby operation of the device will not be adversely affected by contamination build-up. It is also important that the fluid flow rate control device be capable of maintaining a closed condition under vibration and power-loss conditions. The fluid controlled by devices of this type is often under high pressure, tending to maintain the valve in its closed condition, but also establishing a very high head pressure closing force which the valve opening mechanism structure must overcome when opening the valve from a closed position. It is preferable that the valve opening mechanism provide variable "lead", or "lift per revolution" i.e. to provide increasing axial movement in the opening direction in response to a constant rotation of the rotor, thereby to provide maximum force to operate the poppet in an axial direction initially when the fluid pressure is its greatest, and to thereafter reduce the poppet operating force as the valve opens and the fluid pressure reduces.